1. Field of the Invention
This invention relates to new and improved built-up roofing membranes and systems using high-strength glass fiber mats.
2. Description of the Prior Art
Built-up roofing ("BUR") membranes and systems are used primarily on commercial buildings, and used to the substantial exclusion of other roofing types on large industrial buildings of low profile. Its popularity arises from its relatively low cost combined with its effectiveness as a weather repellant surface and its durability. The major drawback in its use is that very high strengths are required, substantially exceeding those of roofing shingles for residential construction. These rigid requirements arise because built up roofing systems are subject to severe stresses induced internally or externally by the surrounding atmosphere, including expansion caused by the presence of moisture internal to the system, and both expansion and contraction forces caused by variation in ambient temperature conditions. For these and other reasons, it is essential that built up roofing systems posses both excellent tear resistance and tensile strengths.
A built-up roofing system is conventionally constructed by (1) applying multiple layers or membranes which are parallel strips of asphalt, impregnated felt in succession onto a rigid roof base, with appropriate overlapping at the joints between adjacent parallel strips used to form a single layer from rolls of the felt, and (2) covering each layer of felt in succession with a coating of fluid hot asphalt and adhesives onto which coating the succeeding layer of felt is applied and adhered before the hot asphalt has cooled to solid form. When the rigid deck for the roofing is a wooden material, for example plywood, it is customary to fasten the bottom layer of felt to the deck with suitable nails. When the deck is concrete, gypsum board, or other material unsuitable for nailing, a bottom coating of primer asphalt is applied thereto to fasten the bottom felt layer to the deck. The top layer of felt receives a final coating of asphalt which optionally is protected by a layer of loose aggregate imbedded in and covering the asphalt.
In the past, most roofing products were made of organic rag felt impregnated with asphalt. However, organic felt is not fire-resistant and it is expensive to manufacture. Accordingly, the industry has looked to glass fiber mats to replace organic felts in this application. Prior art roofing products using glass fiber mats are described in U.S. Pat. Nos. 4,129,674; 4,135,022 and 4,135,029. Unfortunately, the built-up roofing products using such glass fiber mats of the prior art, which rely upon continuous strands or elongated, rod-like bundles of fibers as reinforcing agents, often are expensive and difficult to make, or do not possess the high-strength properties, particularly desired for built-up roofing application.
Therefore, it is the object of this invention to provide new and improved built-up roofing membranes and systems, which can be manufactured economically using high-strength glass fiber mats, and which satisfy the rigid standards required of such products. In particular, a feature of this invention is the provision of such products which possess a unique combination of tear resistance and tensile strength, and which can be manufactured using inexpensive raw materials at a rapid rate of production.